Not applicable.
(1) Field of the Invention
The present invention relates to marine vehicles and more particularly to lateral thrusters for use therein.
(2) Description of the Prior Art
Marine vehicles often are required to maneuver at very low speeds and hover in currents. Marine vehicles typically use rudders or other control surfaces to produce maneuvering forces. However, flow over the control surfaces is required to produce a maneuvering force and these forces vary with the square of the vehicle speed. Therefore, at low speed, control surfaces become ineffective. Typically, lateral tunnel thrusters are located in the bow or stern of marine vehicles to meet the low speed maneuvering requirements. However, the effectiveness of tunnel thruster decreases with forward velocity of the vehicle. Often there is an intermediate vehicle speed at which neither the control surfaces nor the thruster produce effective maneuvering forces.
Conventionally, thrusters make use of a rotating propeller in a tunnel through the vehicle. The rotating propeller creates a pressure differential across the blades and drives a jet of water through the tunnel and out one side. The integrated pressure force on the blades is transferred to the vehicle via the rotor hub and force acting in the opposite direction of the jet flow. This effect is used to maneuver the vehicle. In the current art thrusters are designed to be reversible and so that the vehicle may be maneuvered in either port or starboard directions. For most applications, thrusters are designed which are reversible so that the vehicle may be maneuvered in either port or starboard directions.
Early efforts to measure the effects of forward vehicle velocity on tunnel thruster performance have shown that as the forward velocity was increased to speed on the order of 3 knots, the effective side force (force perpendicular to the vehicle axes) from the tunnel thruster decreased to as low as 10 percent of the side force measured at zero maneuvering effectiveness as forward vehicle velocity. Thus with the current art tunnel thruster quickly lose their maneuvering effectiveness as forward vehicle velocity increases.
Experiments conducted to understand this phenomenon indicated that the forward velocity on the vehicle significantly increases fluid velocity through the tunnel for a fix rotor speed. This results in the propeller blade operating off design and unloading the blades, which results in less thrust on the vehicle.
Tunnel thrusters are typically reversible. That is, the blades can be rotated clockwise or counter clockwise to produce a jet in either direction to maneuver the vehicle. Thus any device that is deployed to mitigate the effects of forward velocity must also be reversible.
Various specific arrangements of tunnel thrusters are shown in the prior art.
U.S. Pat. No. 3,686,485 to Wiley et al. discloses a method and apparatus for controlling the thrust delivered by each propeller of a marine propulsion system of the type having a plurality of controllable pitch propellers driven by a common power source. In response to electrical signals supplied to define commanded thrust levels for the propellers, the power source is controlled to provide the power necessary to satisfy the power requirements of the propulsion system and the propeller pitches are individually set so that each propeller absorbs only its proportionate share of the power.
U.S. Pat. No. 3,895,598 to Blickle discloses a ship propulsion unit comprised of a variable pitch propeller supported in a hub mounted on the lower end of a hollow member which is pivotably supported in a fixed housing such that the hollow member and hub are both pivotable about a vertical axis. A coaxial drive shaft for the propeller is enclosed within the hollow element. A plurality of pairs of sealing rings are provided between the hollow member and a portion of said fixed housing to define a plurality of annular chambers through which pass a number of supply and return lines for several fluid pressure systems which lead to the propeller and a servo motor for adjusting the pitch of the propeller blades.
U.S. Pat. No. 4,055,947 to Gongwer discloses an axial flow turbomachinery having an impeller with a plurality of contoured blades mounted within a diffuser throat and about a central rotatable hub. This blade shape is defined by the ratio of the blade root and tip chords to the minimum midsection blade chord, which is between about 1.25 and about 2.25. The ratio of the blade pitch at the root and tip sections as compared with the blade midsection pitch is preferably between about 1.0 and about 1.4.
U.S. Pat. No. 4,470,364 to Kitaura et al. discloses a side thruster for a ship, which includes a propeller mounted in a cylindrical tunnel formed on the ship, and a housing-support is connected between the propeller and the hull of the ship for supporting the propeller in the tunnel. The housing-support extends substantially transversely of the direction of water flow through the tunnel, and it is generally elliptical in cross section. At least one enlargement is firmed on the outer surface of the housing-support for reducing the effect of Karman vortexes, and the enlargement preferably spirals around the outer surface of the housing-support.
U.S. Pat. No. 5,226,844 to Muller discloses a drive for a boat with a propeller hub rotatable about a main axis extending in a normal travel direction, a plurality of blades projecting generally radially of the main axis from the hub and each pivotal so as to be of variable pitch, and respective blade rods extending axially and displaceable axially relative to the hub to vary the pitch in the direction from the hub and nonrotatable about the axis rotatably supports a cylinder housing that is releasably connected to the rods for joint axial movement therewith. A piston displaceable along the axis in the cylinder is releasably connected to the hob for joint axial movement therewith. Pressurizable lines extending through the stator are connected to the cylinder for alternately pressurizing the piston and thereby relatively axially shifting the rods and hub.
U.S. Pat. No. 5,249,992 to Schneider discloses an integral marine propulsion unit utilizing both collective and cyclic propeller blade pitch angle variations to generate a thrust vector in any of three degrees of motion for use with both the submersible and surface marine vessels. The present marine propulsion unit eliminates the need for extraneous drag generating control surfaces and rudders for motion control of a marine vessel by incorporating a flat plate mechanism which includes an Oldham coupler to a pair of plates and a slotted plate coupled with one of the plates. The slotted plate and the one plate coupled to the slotted plate are relatively rotatable about a fixed axis. The flat plate mechanism permits relative angular displacement between the slotted plate and the one plate to collectively pivot all of the propeller blades and permits radial movement of the clotted plate along with propeller blades.
U.S. Pat. No. 5,501,072 to Plancich et al. discloses a thrust propulsion mechanism for a boat including an outlet conduit extending athwartships from a first outlet port in the hull. A paddle-wheel impeller is mounted within the hull for rotation about an axis of rotation by a reversible motor. A circumferential paddle portion of the paddle-wheel impeller extends into an aperture defined centrally in the top wall of the outlet conduit. An inlet conduit extends athwartships form a first inlet port to a second inlet port, and intermediate thereof supplies water to the center of the paddle-wheel impeller. Water is discharged from the paddle-wheel impeller through one of the outlet ports, dependent on the direction of rotation of the paddle-wheel impeller, to create thrust by a combined paddle wheel and centrifugal pump action.
U.S. Pat. No. 5,522,335 to Veronesi et al. discloses an auxiliary thruster for a marine vessel. The auxiliary thruster includes a submersible propulsion unit which has a shroud with a propeller rotatably mounted therein. A canned electric motor is mounted between the propeller and the shroud for rotating the propeller to create thrust. A propulsion unit deploying and rotating mechanism is mounted on the hull and on the propulsion unit. The propulsion unit deploying and rotating mechanism is operable to extend the propulsion unit out of the hull and retract it into the hull and to rotate the propulsion unit to direct the thrust generated thereby in any desired direction when the thruster is in the deployed position. When the thruster is retracted, it is positioned with a tunnel extending transversely through the hull. Rotation of the propeller while in the retracted position generates laterally directed thrust through the tunnel.
An object of this invention is to improve the control performance of tunnel thrusters at intermediate forward speeds and thus fill the gap in maneuvering effectiveness.
The present invention is a marine vehicle having enhanced maneuverability that has hull at least partially submerged in fluid, which will ordinarily be water. The vehicle has a forward bow, a longitudinal axis extending rearwardly from said bow and opposed first and second sides. The first and second sides have respectively a first major opening and a first small opening and a second opening. A fluid-conducting tunnel extends generally transversely through the hull from the first major opening on the first side of the hull to the second major opening on the said side of the hull. There is a propeller for causing fluid to flow through the tunnel. In order to compensate for the detrimental effect on thrust caused by increases in forward vehicle velocity (Vv), rotor speed (N) of the propeller is increased proportionally to measured increases in axial fluid velocity (Vx).